Tropical Storm Barry – Sunday Update

Barry is still considered a tropical storm right now by NHC, even though its maximum winds are out over open waters of the Gulf of Mexico. These winds are far from the center of circulation and lowest pressure near Shreveport, Louisiana, where winds are slowed by friction and thunderstorms are not as intense. Winds over most of south Louisiana as of 2 pm had dropped to 25-35 mph.

The big story with Barry now is the rain it is producing. The regional radar composite above shows a near solid wall of rain over the state of Mississippi, extending into much of eastern Louisiana and eastern Arkansas. Along the eastern edge of the area of heaviest rain, bands of thunderstorms are forming over parts of western and southern Alabama, and these may spread into central Alabama later today. There are also a few bands of thunderstorms over northern Georgia.

Some parts of south MS, extreme south AL, and southwest LA have already received 3-8″ of rainfall from Barry, and some rivers are already flooding. As Barry’s pressure continues to rise and the circulation weakens over the next 48 hours, the mass of rain will slowly decrease in size and intensity. But, even by Tuesday, with tropical moisture in place over the Southeast US, scattered afternoon storms will be increased, and some heavy rainfall amounts will occur from Memphis to Nashville and Paducah. The NOAA total rainfall forecast for the next 7 days reflects this increase centered near Memphis, with amounts over 7″ centered there, and amounts over 4″ expected in Little Rock, Paducah, and Jackson, TN. Rainfall amounts will drop off dramatically to the east over AL, middle and eastern TN, and GA, where less than 2″ is expected. Given the alignment of the rain maximum, some flooding along the Mississippi River, especially from Cape Girardeau south, is likely.

NOAA forecast 7-day rainfall starting now

One more interesting thing being picked up by upper-air weather balloons and computer models is the warm air aloft associated with Barry. Even though it has weakened to tropical storm winds, one can still see that temperatures at 500 mb (about 18,000 feet) are 10 to 15 degrees warmer above Barry than at other locations even over the Southern United States and the Gulf of Mexico. It is this warm air aloft, produced by the latent heat release in thunderstorms, that causes the air aloft to be lighter, and therefore cause the low pressure at the surface that drives tropical systems like hurricanes.